Thermoset resins have been used in many varieties of fiber-reinforced composites to make parts and articles used in automobiles, aircraft, watercraft, wind turbines, construction materials, and many other types of equipment. Prior to curing, many of these resin compositions have relatively low viscosity, making them easy to mix with glass fibers and pellets to form a curable amalgam that is hardened into the final fiber-reinforced composite.
Typically, the resin compositions include polymerizable organic compounds and one or more agents that facilitate the polymerization of the organic compounds under curing conditions. In many instances, the agents are mixed with the polymerizable organic compounds just before the resin composition is introduced to the fibers. When the agents are mixed too early with the polymerizable organic compounds, they tend to cure prematurely and have to be discarded. In other words, the curable resin composition that includes both the polymerizable organic compounds and the requisite polymerization agents tend to have a relatively short shelf life or pot life.
In many instances, even if the pot life of the mixture of agents and polymerizable organic compounds is long enough to permit pre-mixing before the resin composition is introduced to the fibers, low threshold temperatuers are required to prevent premature resin curing. At lower temperature, the resin composition typically has a higher viscosity that requires higher processing pressures when forming the resin-fiber amalgam.
The short pot life and low threshold temperature of the resin compositions can create many difficulties in the manufacturing process. For example, production slowdowns caused by equipment breakdowns and clogs, quality control checks, and adjustments during manufacturing can waste large quantities of a prematurely hardening resin composition. These breakdowns are generally more frequent when the system is stressed by low-temperature, high-viscosity resin compositions. Because most thermoset resins are not recyclable like metal and glass, the hardened resins cannot be recovered. The short pot life often requires rapid mixing of the polymerizable organic compounds with the polymerization agents. This can require additional processing equipment to monitor and maintain a homogeneous resin composition just when it's needed during manufacturing. Thus, there is a need for new manufacturing methods to produce fiber-reinforced resin composites that reduce or eliminate the problems created by the short pot life and/or low threshold temperatures for many thermoset resin compositions. This and other problems are addressed in the present application.